If you always forget to change your razor blade in time and those blue stripes doesn’t help much, here’s a simple trick.
Write it down!
I use a Gillette, where new blades are stored under the stand in a special disposable container. Use a permanent marker to right above the slot as you empty it.
Gillette cartridges are good for about 10-12 shaves, depending on you facial hair type. If you you shave on weekdays only, you should install a fresh blade every two weeks. So write the date when you installed it or the date when to change it, and free your brain for more important things.
Here are my results.